1. Field of the Invention
This invention relates generally to the use of block copolymers (BCPs) to make a chemical contrast pattern, and more particularly to the use of the chemical contrast pattern as an etch mask for pattern transfer into a substrate.
2. Description of the Related Art
Directed self-assembly (DSA) of block copolymers (BCPs) has been proposed for making imprint templates. Imprint templates have application in making patterned-media magnetic recording disks and in semiconductor manufacturing, for example, for patterning parallel generally straight lines in MPU, DRAM and NAND flash devices. DSA of BCPs by use of a patterned sublayer for the BCP film is well-known. After the BCP components self-assemble on the patterned sublayer, one of the components is selectively removed, leaving the other component with the desired pattern, which can be used as an etch mask to transfer the pattern into an underlying substrate. The etched substrate can be used as an imprint template.
More recently a method termed “sequential infiltration synthesis” (SIS) uses a BCP and atomic layer deposition (ALD) to selectively grow nanometer scale patterns of inorganic material inside BCP. In SIS, a BCP film is deposited onto a substrate and annealed to form a self-assembled pattern of the two BCP components. In one example, the BCP is poly(styrene-block-methyl methacrylate) (PS-b-PMMA). A first precursor for the inorganic material is introduced into the ALD and infiltrates the PMMA but does not react with the PS. A second precursor for the inorganic material is then introduced to finish the reaction, forming the inorganic material, for example alumina (Al2O3), in the locations in the PMMA where the first precursor attached. The PS and PMMA are removed, leaving a pattern that generally replicates the original pattern of PS and PMMA but that is now made of the inorganic material synthesized by the ALD precursors. This pattern of inorganic material can then be used as an etch mask to etch the substrate.
While the conventional SIS method provides a way to use the distinct chemistries of the constituent components of a BCP film to grow materials by ALD on specific locations, the density of active sites where the ALD precursor can bind is extremely low, especially when using the method to achieve dimensions down to a few nanometers. It has been found that after removal of all of the polymer material (the PS and PMMA in the above example), the amount of inorganic material (alumina in the above example) is not sufficient to make a robust etch mask. This is because the remaining features may be discontinuous or may have shifted as the PS and PMMA is removed, thus degrading the image quality of the original pattern.
What is needed is a method for making a chemical contrast pattern with BCPs that uses SIS but that does not result in a pattern with discontinuous or shifted features.